1. Technical Field
The present invention relates generally to electronic signal connectors and, more particularly, to a backshell configuration for providing a mechanical connection for communicating signals in a rigorous vibration environment.
2. Background Information
Electrical connections are commonly used in transmitting signals and data between computers, systems and other devices. Typically, one device is connected to another device or system through a single wire or multiple wires. In many instances, a cable bundle containing these wires terminates in a mechanical housing, also known as a backshell, which provides physical protection for each wire in the cable bundle to each pin in an apparatus for making mated connections in the connected device. A backshell also protects the wires and connectors from fatigue. For example, FIG. 1 shows a typical prior art connection between a device 10 and a cable bundle 20 containing multiple wires 22. The cable bundle 20 terminates in a mechanical housing also known as a backshell 30. Generally, some form of mechanical connection is provided to prevent the backshell from becoming disconnected from the connected device and to maintain the signal contact at all times. For example, in the exemplary embodiment shown in FIG. 1, two No. 4 size screws 40 are provided with thumb adjustment knobs to provide this mechanical connection.
U.S. Pat. Nos. 4,579,415, 5,348,482, 5,788,528, 5,855,493, 5,911,595, 5,961,348 discuss typical backshell constructions, magnetic grounding techniques in backshells, cable strain relief techniques, and the cabinets to which the backshell connectors may be attached. The general functionality of these patents is incorporated by reference as background information.
While this sort of connection may be sufficient in some applications, a large number of situations exist where the environment provides particularly challenging conditions which may cause the mechanical connection to fail. The failures may be a permanent disconnection of the wires resulting in a permanent interruption in the signals being transmitted or communicated, or may be temporary or intermittent open circuits which distort or destroy the signal integrity. In many applications, even a momentary disruption in signal integrity can have very undesirable results.
Electrical connections which are made between avionics devices are often subject to a rigorous vibrational environment. For example, helicopters and fixed-wing aircraft experience a broad range of vibrations and temperature swings. These vibrations may loosen the connectors 40 over a period of time, such as by unscrewing or stripping the threads of connectors 40. Also, the small No. 4 size screws 40 can slip and fail to maintain the connection under rigorous environmental conditions. Furthermore, the vibrations may cause the connection point between the wires of the device and the wires in the backshell to disengage unless constant pressure keeps the wires held together. Although the present discussion focuses primarily on the rigorous vibrational environments found in fixed-wing aircraft and helicopters, similarly challenging environments may be found in pumps, fans, motors, and other large machinery found, for example, on oil rigs, shop floors, and other such high vibration applications. Furthermore, connections between cable bundles and electrical devices may be challenged by other environmental factors such as high temperatures, or large temperature changes, low and high humidity conditions and electromagnetic radiation environments. For all of these conditions, it is desirable to have a strong mechanical connection to maintain signal integrity.
Connections in avionics devices typically use an ARINC 404 connector such as, for example, a DPX model connector available from Cannon, mil number, MIL-C-81659. ARINC stands for Air Radio Inc. ARINC 404 is a specification, known to those of skill in the art, that defines air transport avionics equipment interfaces. ARINC 404 connectors tend to perform well in the high vibration environment found in avionics. However, due to the use of smaller and lighter devices and systems in aircraft, some manufacturers have moved away from the ARINC 404 connectors and have begun manufacturing devices that require connectors such as the D subminiature connectors. These D subminiature connectors, when attached by methods of the prior art, may not be mechanically robust and may lack the ability to provide a reliable signal. Furthermore, the prior art D subminiature type connectors are bulky, often difficult to install, and lack packaging efficiency.
The trend in avionics is to use smaller and lighter components to improve the performance of aircraft. Thus, manufacturers have combined multiple devices into smaller packages. One difficulty that has been encountered with the use of the D subminiature connectors is that cabinet 15 (such as the cabinet illustrated in FIG. 1) which contains one or more devices 10 is typically very small and leaves little room for accessing the thumb screws 40. Moreover, standard backshells are a difficult fit in congested avionics bays.
The tight spacing tolerances also make it difficult to use the standard D subminiature connectors because in some situations, the cabinet 15 may be located so close to device 10 that, although there is room for the backshell 30 between the device 10 and cabinet door 16, there may not be room for the cable bundle 20 to come out of end 32 of backshell 30 so as to not interfere with the closing of the cabinet door 16. This interference, for example, can be shown in FIG. 1 at interference point 28. It will be readily appreciated, however, that if cable bundle 20 exits backshell 30 on either top side 34 or bottom side 36, it would be more difficult to access connectors 40 to tighten backshell 30 to device 10. In some situations, more than one connector is attached to the device 10. When these connections are in line and close together, it is harder still to obtain access to the mechanical fasteners.
Moreover, the screws 40 used to attach standard D subminiature connectors are limited to the small No. 4 size screws that fit into standard D subminiature threaded screw receiving holes in the mating D subminiature connector. Therefore, it has been difficult to provide a means of mating the D subminiature connector with any other fastener other than these small screws, and it has thus been difficult to form a connection which can withstand the rigorous vibration environments found in aircraft avionics bays.
Therefore, a need exists for an integrated backshell that fits the tight confines of avionics bays while allowing access to the connectors. A further need exists for an integrated backshell that accommodates multiple connectors for efficient use of space, simplification of making connections, and added assurance of making the connections at the right places. There is a further need for a strong mechanical connection that can withstand a rigorous vibrational environment.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can only be gained by taking the entire specification, claims, drawings, and abstract as a whole.
In an exemplary embodiment, a back shell is provided for forming an electrical connection with a cabinet, the backshell comprising at least one electrical connector, such as a D subminiature connector, a deflection arm coupled to one end of the back shell for engaging a cam on a cabinet which holds a receiving connector, and a fastener, for example, a captive mechanical jackscrew, on the opposite end of the backshell from the deflection arm. The deflection arm provides a clamping force when the fastener is fully engaged, and helps form a strong mechanical connection. In another exemplary embodiment, a mechanical jackscrew is provided on both ends of the backshell for securing the backshell to the cabinet.
The novel features of the present invention will become apparent to those of skill in the art upon examination of the following detailed description of the invention or can be learned by practice of the present invention. It should be understood, however, that the detailed description of the invention and the specific examples presented, while indicating certain embodiments of the present invention, are provided for illustration purposes only and that various changes and modifications within the spirit and scope of the invention will become apparent to those of skill in the art from the detailed description of the invention and claims that follow.